Authorities in Nepal warned of possible fresh flooding on Sunday, urging residents in already devastated districts to remain on high alert, as mountain rescue specialists more usually deployed to assist climbers on peaks including Everest joined the search for hydropower workers trapped in flooded tunnels.
Flood warning notices were sent to residents' phones throughout the morning after water levels rose in the Bhotekoshi river, as rescue crews worked to clear a major highway connecting Kathmandu to one of the worst-hit areas.
The combined death toll in Nepal and Tibet has risen to 750, with more than 3,000 people still missing, authorities said on Sunday.
Nepal's disaster agency put the toll in the country at 734, with 2,498 missing, while Chinese authorities reported 16 deaths and 546 missing on the Tibetan side of the border, including more than 100 Nepalis and people from over a dozen other countries.
Army rescue teams drilled into the upper part of a mud-filled tunnel at the Trishuli 3A hydropower site on Saturday evening, breaking through far enough to begin pumping in air and lowering a camera. However, heavy overnight rain and rising river levels have since hampered further progress.
"Heavy rainfall after around 2am caused the water level in the river to rise, and also fill in the excavation area," the Nepal Army said on Sunday morning, as the rescue operation entered its fifth day.
People try to enter their damaged house following deadly flash floods and mudslides, in Devighat, Nuwakot district, Nepal (Reuters)
The trapped workers are among 933 people employed at hydropower projects reported missing since Wednesday's flood, according to Nepal's National Disaster Risk Reduction and Management Authority, with efforts also focused on the Trishuli 3B site.
Nepal's prime minster's office said that teams faced "continuous rainfall and difficult conditions" but had worked nonstop overnight "making tireless efforts to search for and rescue those who may be trapped."
The rescue teams are using advanced search cameras and specialised monitors, it added.
Specialised tunnel-rescue teams from India and China have joined the operation, alongside Nepal's own mountain rescue specialists, who have been deployed to a separate damaged hydropower site.
The latest flood warnings followed Chinese authorities alerting their Nepali counterparts to increased water flow upstream, Dharam Raj Uprety, chief executive of Nepal's National Disaster Risk Reduction and Management Authority, told the Associated Press.
In the town of Galchhi, a group of residents sought higher ground on a nearby bridge and watched the river roar past, pointing to enormous boulders that had been washed downstream during Wednesday's floods, as others standing on a suspension bridge over the water were warned off with whistles.
Along the river, entire homes, vehicles and farm tractors could be seen jutting from the thick grey-brown sediment that has enveloped villages in the worst-hit areas, and rice terraces along the riverbank have collapsed into the water after landslides.
A drone view of the aftermath of flash flooding along the Trishuli river amidst fresh water surge warning in the Trishuli Bazaar area of Nuwakot district, Nepal (AP)
